P0124

Throttle Position Sensor/Switch A Circuit Intermittent

P0124 is a generic OBD-II powertrain diagnostic trouble code: Throttle Position Sensor/Switch A Circuit Intermittent. It is logged by the engine control unit when the throttle monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0124
Group
Powertrain
System
Throttle
Severity
Warning (MIL on, possible limp mode)
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What P0124 means

P0124 is stored when the PCM detects an intermittent or erratic signal from the throttle position sensor (TPS) or accelerator pedal position (APP) sensor circuit 'A'. Unlike P0122/P0123 which indicate a continuously out-of-range voltage, P0124 means the signal is valid most of the time but periodically drops out or spikes to an implausible value. Because the PCM uses TPS/APP data to determine throttle opening rate, fuel delivery, and transmission shift points, even momentary signal loss can cause sudden hesitation, stumbling, or — in drive-by-wire systems — a brief entry into reduced-power (limp) mode.

The intermittent nature makes P0124 notoriously difficult to diagnose. The throttle body and pedal assembly are both mounted at points that experience significant vibration and mechanical flex; the wiring harness routing through these areas is a primary suspect for chafe against brackets or pivot points. A thorough wiggle test along the entire TPS/APP harness — from the sensor body back to the PCM — while monitoring live TPS voltage on a scan tool or oscilloscope is the most reliable diagnostic technique. Harness sections near the throttle body pivot, firewall grommet, and rubber grommets passing through the engine bay are common chafe locations.

Connector pin tension is frequently overlooked: a spread or backed-out terminal pin passes continuity tests but loses contact momentarily under vibration. Back-probe each pin and check for voltage dropout while flexing the connector body. If a drive-by-wire vehicle enters limp mode repeatedly without a permanent code, a pending P0124 should be the first suspect after ruling out battery and ground integrity.

Common causes

Most-frequently reported root causes when P0124 is logged.

  • 1
    Loose, corroded, or spread terminal pins in the TPS or APP sensor connector causing momentary signal loss under vibration.
  • 2
    Chafed TPS/APP wiring harness where it passes near the throttle body pivot bracket or a firewall grommet.
  • 3
    Failing TPS or APP sensor with an internally worn resistive track producing intermittent voltage dropouts.
  • 4
    Carbon buildup or mechanical binding in the throttle body causing the sensor to skip across its range.
  • 5
    Open or high-resistance signal circuit from a hairline wire break inside intact insulation.
  • 6
    Poor PCM ground or reference voltage instability causing the 5 V supply to momentarily sag.
  • 7
    Water or moisture ingress into the connector producing transient resistance changes.

Symptoms drivers notice

Check engine light on; may be stored rather than active if the fault cleared before the next drive cycle.
Intermittent hesitation, stumble, or flat spot during acceleration that self-resolves within seconds.
Occasional brief entry into limp/reduced-power mode in drive-by-wire vehicles, with normal operation resuming automatically.
Unstable idle — RPM hunting briefly before stabilising.
Unpredictable engine response when modulating the throttle at part load.
No fault reproduced on a short workshop test drive — the vehicle performs normally.

How to diagnose P0124

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve freeze-frame data and note throttle position, RPM, and vehicle speed at the moment of fault to characterise the conditions under which the signal glitched.
  2. 2
    With the engine running and live TPS voltage displayed on a scan tool, perform a slow sweep of the throttle pedal while watching for dropouts — valid range is typically ~0.45 V at idle to ~4.5 V at wide-open throttle; any spike or void is a fault indication.
  3. 3
    Perform a wiggle test along the full TPS/APP harness — from sensor to PCM — while watching live voltage; pay particular attention to sections passing near the throttle pivot, firewall grommet, and any rubber harness isolators.
  4. 4
    Inspect all connector pin tension by backprobing each terminal and gently flexing the connector body; a spread or pushed-back pin will drop voltage under light flex.
  5. 5
    Check harness routing for chafe against metal brackets, pivot points, or moving engine components; apply split loom or reroute as needed.
  6. 6
    Use an oscilloscope if available — it captures sub-millisecond dropouts that a scan tool's 100 ms refresh rate will miss, revealing a glitch that a multimeter continuity check alone cannot detect.
  7. 7
    If wiring and connector are confirmed good, substitute a known-good TPS/APP sensor and complete several heat cycles including a road test before condemning the original sensor.

Related powertrain codes

Frequently asked questions

Is P0124 dangerous to drive with?

Potentially yes. An intermittent throttle position signal can cause a sudden loss of power or hesitation in traffic, which is a safety risk. On drive-by-wire vehicles the PCM may also engage a reduced-power or limp mode unexpectedly. Diagnose and repair P0124 before regular highway driving.

Why does the fault disappear when I bring the car to a mechanic?

Intermittent faults often require specific conditions — a particular engine temperature, road vibration at highway speed, or throttle input at a specific angle — to reproduce. Static workshop testing rarely recreates these. Request a road test with scan tool data logging or ask the technician to monitor live TPS voltage during a highway drive.

Could a dirty throttle body cause P0124?

Indirectly, yes. Significant carbon deposits can cause mechanical binding or stiction in the throttle plate, forcing the TPS to jump abruptly across its range rather than sweep smoothly. This can produce signal spikes the PCM reads as intermittent. Throttle body cleaning is a reasonable and low-cost first step before investigating electrical faults.

Can P0124 appear on both cable-actuated and drive-by-wire throttle systems?

Yes. On cable systems P0124 refers to the throttle position sensor on the throttle body. On drive-by-wire systems it can refer to either the throttle body TPS or the accelerator pedal position sensor — some vehicles use a dual-track APP sensor where 'A' is one of two tracks. Identify which sensor and circuit 'A' refers to on your specific vehicle using the service manual.

Disabling P0124 in software

RaceTune can permanently disable P0124 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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